Capsular polysaccharides are important virulence factors for pathogenic bacteria and are immunogens against bacterial disease. The objective of this project is to understand the chemistry of this polysaccharide and to use this chemistry to (a) develop glyconconjugate vaccines against bacterial disease and (b) understand the structure of these glycoconjugates and how they interact with the immune system. Based on this approach a chemoenzymatic method is being developed to prepare polysaccharide analogs of the poorly immunogenic E. coli K1 polysialic acied. Analogs of sialic acid have been synthesized and feed to polysaccharide producing bacteria lacking the ability to synthesize sialic acid. The immunochemical characteristics of the resulting polysaccharides are being determined.